Petroleum is still the primary feed stock for oil-fired burners for petroleum refineries, petrochemical industries, domestic power generation and for on-site production of steam for reinjection into a well for steam flooding which is a major Enhanced Oil Recovery (EOR) Process being successfully practiced in California and elsewhere.
However, there are very few instances of naturally occurring low-sulfur crudes (less than 0.5% sulfur) and the limited availability makes these crude oils very expensive. Combustion of high sulfur crudes leads to sulfur dioxide emissions at excessive levels which require expensive post-combustion scrubbing of the flue gas.
Pre-combustion desulfurization is an alternative. Sulfur removal from petroleum oil at the site is much more difficult than desulfurization of coal due to the unique organic-sulfur form of the impurity and the EPA requirement to reduce the sulfur content to about 0.3%. Whereas, some coals mainly contain pyritic sulfur of the inorganic type which can readily be removed by physical-chemical treatment, it is much more difficult to remove organic thiophenes from petroleum. Organic thiophenes are mainly liquids and tend to co-distil with the petroleum fraction if fractionation purification is attempted.
Hydrodesulfurization of petroleum crude oil with cobalt-molybdenum or nickel-molybdenum catalysts on an alumina support is a currently utilized desulfurization process. The requirements of catalysts, hydrogen consumption and severe reactor operating conditions render this process quite expensive. An urgent need for an economical, crude oil desulfurization process has been expressed by the petroleum industry in a recent survey.